Internal Combustion Engines: What is It and How It Works

An engine in which the chemical energy of the fuel is released inside the engine and is converted into mechanical work can be defined as an internal combustion engine (Ferguson and Kirkpatrick 2015).

An increase in pressure is caused due to the combustion of fuels such as diesel or petrol in the combustion chamber. This drives down the piston and through this process, chemical energy is converted into mechanical energy.

A Few Highlights

• In 1876, the first practical four-stroke engine with in-cylinder compression was developed by Nikolaus Otto, a German engineer and it was named the “Otto Silent Engine”.
• However, the concept of a four-stroke engine had been conceived and patented by A. de Rochas in 1861.
• Sir Dugald Clerk, a Scottish mechanical engineer invented and built the first two-stroke engine, which he then patented in 1881.
• A German engineer, Rudolph Diesel, developed the first four-stroke engine that used the direct injection of liquid fuel into the combustion chamber. Auto-ignition and combustion of the fuel air mixture were the results of the high compression ratio of the engine (Ferguson and Kirkpatrick 2015).

How it Works (Two Stroke Engine)

• In a two-stroke engine, the functions performed are the same as a four-stroke engine, but it does so in just two piston strokes or “steps” as opposed to four.
• In the simplest two-stroke engines, this is done by using the crankcase and the underside of the moving piston as a pump for the fuel-air mixture. The official name given to such engines is “crankcase-scavenged two-strokes.”
• Just below Top Dead Center (TDC), the spark plug releases a spark and combusts the fuel. This combustion produces enough energy to push the piston down.
• While the piston nears Bottom Dead Center (BDC), the mixture of air, fuel and oil continues to move up the transfer ports, and into the cylinder. As the piston rises, it first covers the transfer ports and leaves only the exhaust port open so as to allow exhaust gases to leave the combustion chamber.
• Oil is mixed with within the fuel as it is not possible to lubricate the parts of the engine in any other way. This leads to unburnt oil which is recognizable through black smoke exiting the exhaust of the vehicle as well as a distinct smell of petrol.

There are 4 distinct strokes in a 4-stroke engine. They are:

1. Intake
2. Compression
3. Expansion
4. Exhaust

• Stroke 1: Intake - An intake valve opens in order to let in air, or an air-fuel mixture. The downwards movement of the piston creates suction. As a result of the suction, the air/air-fuel mixture moves into the combustion chamber. In order to maximize the amount of fresh mixture inducted, the intake valve opens just before the stroke starts and closes just after the stroke ends.
• Stroke 2: Compression - The mixture is compressed to a fraction of its original volume. For this stroke to be most effective, the intake and exhaust valves must remain closed. Combustion is initiated toward the end of this stoke which leads to a rapid increase in cylinder pressure.
• Stroke 3: Expansion – As a result of the compression stroke, the mixture is highly pressurized which results in the piston being pushed down to bottom dead center (BDC), which forces the crankshaft to rotate. Once the piston reaches BDC, the exhaust valve opens in order to initiate the Exhaust stroke
• Stroke 4: Exhaust – In this stroke, all of the burned fuel leaves the combustion chamber in order to make space for fresh mixture. In order to ensure all the burned fuels, leave the system, the piston moves towards top dead center (TDC). Just before TDC, the exhaust valve closes and the intake valve opens restarting the cycle of the four strokes.